1. Field of the Invention
The present invention relates to a liquid ejector configured to eject, from nozzles, liquid in the form of liquid droplets.
2. Description of the Related Art
In an ink-jet printer, there are required reducing a size of an ink-jet recording head and reducing sizes of liquid droplets for enhancing a speed of recording and improving a quality of a recorded image, so that sizes of pressure chambers and nozzles of the recording head are reduced. For example, Patent Document 1 (Japanese Patent Application Publication No. 2004-154962) discloses a recording head including (a) a channel unit constituted by a plurality of thin plates which are stacked on each other and in which the pressure chambers, the nozzles, and so on are formed and (b) a piezoelectric actuator stacked on the channel unit. In the piezoelectric actuator, there are provided electrodes which are independent of each other, and each of which overlaps with a central area of a corresponding one of the pressure chambers in plan view. Piezoelectric layers in the actuator are deformed relative to the pressure chambers by applying voltages to the electrodes.
When the liquid droplet is ejected from each of the nozzles, a technique generally called a “fill-before-fire” is employed to obtain a relatively high velocity of ejection by relatively small voltage for driving the recording head. In the “fill-before-fire” technique, the liquid is ejected in the following manner. Pressure fluctuation is generated in the liquid in the pressure chamber by changing a state of the pressure chamber from a volume-reduced state thereof in which a volume of the pressure chamber is reduced, to a volume-increased state thereof in which the volume of the pressure chamber is increased. Then, the state of the pressure chamber is returned to the volume-reduced state thereof at a timing when the pressure is relatively high in the periodic pressure fluctuation, whereby a pressure in the pressure fluctuation and a pressure generated by the reduction of the volume of the pressure chamber are superimposed on each other. As a result, the liquid droplet is ejected from the nozzle. Further, when the liquid droplet is being ejected from the nozzle, the volume of the pressure chamber is increased by applying an additional pulse, whereby a trailing end of the liquid droplet is pulled back. As a result, the size of the liquid droplet is reduced.